It is well known in the field of irrigation generally and rotating sprinklers particularly for a sprinkler device to emit a non-rotating stream from a fixed nozzle onto a rotating plate with substantially radial grooves that also establish a moment arm, causing the plate (often referred to as a “rotor plate”) to rotate about the nozzle axis. The plate also reorients the stream from vertical to substantially horizontal, distributing the water in a circular pattern. The grooves of the rotor plate may be configured to produce different wetting patterns, depending on specific site applications. In some cases, the rotation of the rotor plate is slowed by a viscous brake or “motor” in order to maximize the throw radius of the stream. In other cases, the rotor may be of the free-spinning type. Examples of such sprinkler constructions may be found in commonly owned U.S. Pat. Nos. Re. 33,823; 4,796,811; 5,297,737; 5,372,307; 5,439,174; and 5,588,595. An offset rotating nozzle sprinkler incorporating viscous damping is disclosed in U.S. Pat. No. 4,440,345.
It is nevertheless desirable to improve the performance characteristics of such sprinkler devices, and to build in greater flexibility with respect to producing desirable distribution curves in a simpler more cost effective manner.